SEXUAL SELECTION. 



Part IL 



" the intermaxillary bones of tlie upper jaw."^ (Figs. 

 26 and 27.) In our salmon this change of structure 

 lasts only during the breeding-season ; but in the Sahno 

 hjcaodon of N.W. America the change, as Mr. J. K. 



Pig. 26. Head of male of common salmon {Salmo salar) during the breeding-season. 



[This drawing, as well as all the others in the present chapter, have been executed by 

 the well-known artist, Mr. G. Ford, under the kind superintendence of Dr. Glinther, from 

 specimens in the British Museum.] 



6 Yarrell, ' History of British Fishes,' voL ii. 1836, p. 10. 



